Structural Analysis Methods for the Assessment of Reinforced Concrete Slabs

Doktorsavhandling, 2017

Reinforced concrete (RC) slabs are among the most critical parts of the load-carrying capacity of such structures as bridges and parking decks. Previous research indicated that the assessment methods used in current practices largely underestimated the load-carrying capacity. The objective of the study reported in this thesis is to develop and calibrate improved methods for the assessment of load-carrying capacity and the response of RC slabs.
A Multi-level Assessment Strategy has been proposed. The strategy is based on the principle of successively improved evaluation in structural assessment. The strategy includes simplified analysis, linear finite element (FE) analysis and non-linear shell FE analysis, as well as non-linear continuum FE analysis with and without consideration of the interaction between reinforcement and surrounding concrete.
According to the Multi-level Assessment Strategy, enhanced FE analyses have shown to possess great possibilities for achieving a better understanding of the structural response and revealing the higher load-carrying capacity of existing structures. However, non-linear 3D continuum FE analysis, at the highest level of the proposed strategy, is demanding and an analysis involves many modelling choices that are decisive for results. For the purpose of mapping the influence of different modelling choices on the structural behaviour of the FE model of RC slabs, sensitivity analyses have been conducted for RC slabs subjected to bending and especially to shear and punching failure. The selected modelling choices, within five major categories are: geometric non-linearity, element properties, modelling of concrete and reinforcement, as well as modelling of supports. The results show the possibility of accurately reflecting the experimental results concerning load-carrying capacity, load-deflection response, crack pattern and load distribution, given that proper modelling choices are used. Thereafter, the selected modelling choices were applied in FE analyses to investigate the load distribution and several influencing factors, including cracking, flexural reinforcement and the geometry of slabs and supports. The effect of flexural reinforcement and the size of specimens on structural response were also studied.
To examine the previously developed enhanced analysis approach, the Multi-level Assessment Strategy was applied to several laboratory tests and to a 55-year-old field-tested existing RC bridge deck slab, and results were compared to the experiments. The difference between assessment methods at different levels of detail was discussed. The results show that in general, advanced models are more capable of demonstrating load-carrying capacity that better reflects reality. The high-level continuum FE analysis and shell FE analysis coupled with a mechanical model, such as the Critical Shear Crack Theory (CSCT) are capable of predicting the shear and punching behaviour of RC slabs with reasonable accuracy. In addition, the influence of parameters such as boundary conditions, the location of concentrated loads and shear force distribution were found to affect the shear capacity of the field-tested bridge deck slab.